Etching method and plasma processing apparatus

ABSTRACT

An etching method is provided. In the etching method, a silicon oxide film is etched by using plasma in a first condition. In the first condition, a surface temperature of a substrate is controlled to have a temperature lower than −35 degrees C., and the plasma is generated from a hydrogen-containing gas and a fluorine-containing gas by using first radio frequency power output from a first radio frequency power source and second radio frequency power output from a second radio frequency power source. Next, the silicon oxide film is etched by using the plasma in a second condition. In the second condition, the output of the second radio frequency power from the second radio frequency power source is stopped. The silicon oxide film is etched by using the plasma alternately in the first condition and in the second condition multiple times.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based upon and claims the benefit of priorityof Japanese Patent Application No. 2015-126038, filed on Jun. 23, 2015,and Japanese Patent Application No. 2015-248345, filed on Dec. 21, 2015,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an etching method and a plasmaprocessing apparatus.

2. Description of the Related Art

In order to perform a preferable etching in a substrate plasma etchingprocess, a method of controlling a temperature of a surface of asubstrate by using a heater and a cooling mechanism provided in apedestal for receiving the substrate, is suggested. For example, in anetching process described in Japanese Laid-Open Patent ApplicationPublication No. 10-303185, a process temperature that causes a surfacetemperature of a substrate to be maintained during an etching, is lowerthan a plasma heating temperature at which the substrate reaches a stateof thermal equilibrium by being heated by plasma. Hence, the surfacetemperature of the substrate rises due to heat input from the plasma.Hence, Japanese Laid-Open Patent Application Publication No. 10-303185supposes cooling the substrate by a cooling mechanism to keep thesurface temperature of the substrate at the predetermined processtemperature.

However, in Japanese Laid-Open Patent Application Publication No.10-303185, a temperature of a coolant is set at about 20 degrees C. whenthe plasma heating temperature is 300 degrees C. and the processtemperature is 87 degrees C. The disclosure in Japanese Laid-Open PatentApplication Publication No. 10-303185 relates to a substrate surfacetemperature control method in a plasma process under room temperature.Moreover, in Japanese Laid-Open Patent Application Publication No.10-303185, the temperature of the substrate surface is controlled asdescribed above during the etching to solve a problem of what is calleda micro loading. The micro loading is a problem of etching ratedifferences (non-uniformity) depending on hole sizes when etching viaholes, contact holes and the like.

However, because the plasma processes under room temperature and anextremely low temperature environment are different from each other inprocess characteristics and temperature range to be controlled, problemscaused by the heat input from the plasma sometimes differ from eachother, and approaches to solve the problems may differ from each other.

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SUMMARY OF THE INVENTION

Accordingly, in response to the above discussed problems, embodiments ofthe present invention provides an etching method and an etchingapparatus that prevent depth loading and increase an etching rate whenetching a silicon oxide film.

According to one embodiment of the present invention, there is providedan etching method. In the etching method, a silicon oxide film is etchedby using plasma in a first condition. In the first condition, a surfacetemperature of a substrate is controlled to have a temperature lowerthan −35 degrees C., and the plasma is generated from ahydrogen-containing gas and a fluorine-containing gas by using firstradio frequency power output from a first radio frequency power sourceand second radio frequency power output from a second radio frequencypower source. Next, the silicon oxide film is etched by using the plasmain a second condition. In the second condition, the output of the secondradio frequency power from the second radio frequency power source isstopped. The silicon oxide film is etched by using the plasmaalternately in the first condition and in the second condition multipletimes.

Additional objects and advantages of the embodiments are set forth inpart in the description which follows, and in part will become obviousfrom the description, or may be learned by practice of the invention.The objects and advantages of the invention will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims. It is to be understood that both theforegoing general description and the following detailed description areexemplary and explanatory and are not restrictive of the invention asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of an etching apparatusaccording to an embodiment of the present invention;

FIGS. 2A and 2B are diagrams showing an example of a method of applyingradio frequency power LF and a result thereof in an extremely lowtemperature etching according to an embodiment of the present invention;

FIGS. 3A and 3B are graphs showing an example of radio frequency powerLF dependency and transfer gas dependency of wafer temperatures;

FIG. 4 is a flowchart illustrating an example of an etching methodaccording to an embodiment of the present invention; FIG. 5 is a diagramshowing an example of an effect of turning off radio frequency power inan extremely low temperature etching according to an embodiment of thepresent invention;

FIG. 6 is a diagram showing an example of turning off radio frequencypower in an extremely low temperature etching according to an embodimentof the present invention;

FIG. 7 is a graph showing an example of a temperature transition duringan extremely low temperature etching according to an embodiment of thepresent invention;

FIG. 8 is a diagram showing an example of an effect of repetition in anextremely low temperature according to an embodiment of the presentinvention;

FIG. 9 is a diagram showing an example of an effect of radio frequencypower in an extremely low temperature etching according to an embodimentof the present invention;

FIG. 10 is a graph showing an example of a relationship between atemperature of a chamber and an etching rate ER in an extremely lowtemperature etching according to an embodiment of the present invention;

FIG. 11 is a graph showing an example of a relationship between radiofrequency power and an etching rate ER in an extremely low temperatureetching according to an embodiment of the present invention;

FIG. 12 is a diagram illustrating an example of a configuration of atemperature control unit according to an embodiment of the presentinvention;

FIG. 13 is a schematic diagram illustrating an example of aninterferometric thermometer according to an embodiment of the presentinvention;

FIGS. 14A and 14B are diagrams illustrating an example of a temperatureadjustment mechanism according to an embodiment of the presentinvention;

FIG. 15 is a graph showing an example of a relationship between apressure of a heat transfer gas and a temperature of a focus ring in anextremely low temperature etching according to an embodiment of thepresent invention; and

FIG. 16 is a graph showing an example of a relationship between anintermittent etching and a temperature of a wafer according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description is given below of embodiments of the present invention,with reference to accompanying drawings. Note that elements havingsubstantially the same functions or features maybe given the samereference numerals and overlapping descriptions thereof may be omitted.

[Overall Configuration of Etching Processing Apparatus]

To begin with, an etching apparatus 1 according to an embodiment of thepresent invention is described below with reference to FIG. 1. FIG. 1illustrates an example of a vertical cross section of the etchingapparatus 1 according to the embodiment. The etching apparatus 1according to the embodiment is an example of a plasma processingapparatus that processes a substrate by using plasma. Although theetching apparatus 1 according to the embodiment performs a plasmaetching on a wafer, the plasma processing apparatus is not limited tothis application, and may be configured to perform a desired plasmaprocess such as a film deposition process and a sputtering process. Theetching apparatus 1 of the embodiment is configured to be a parallelplate type plasma processing apparatus (capacitively-coupled plasmaprocessing apparatus) in which a pedestal 20 and a gas shower head 25are disposed to face each other in a chamber 10. The pedestal 20 alsofunctions as a lower electrode, and the gas shower head 25 alsofunctions as an upper electrode.

The etching apparatus 1 includes the chamber 10 with a surface, forexample, made of alumited (anodized) aluminum. The chamber 10 isconnected to the ground. The pedestal 20 is installed on a bottom of thechamber and receives a semiconductor wafer (which is hereinafter justreferred to as a “wafer W”) thereon. The wafer W is an example of asubstrate. The pedestal 20 is, for example, made of aluminum (Al),titanium (Ti), silicon carbide (SiC) and the like. An electrostaticchuck 106 for electrostatically attracting the wafer W thereon isprovided on an upper surface of the pedestal 20. The electrostatic chuck106 is configured to have a chuck electrode 106 a sandwiched betweeninsulating bodies 106 b or surrounded by the insulating body 106 b. Adirect voltage source 112 is connected to the chuck electrode 106 a, andattracts the wafer W on the electrostatic chuck 106 by Coulomb' s forceby applying a direct voltage HV to the chuck electrode 106 a.

A focus ring 108 is disposed at a periphery of the electrostatic chuck106 so as to surround the pedestal 20. For example, the focus ring 108is made of silicon or quartz. The focus ring serves to improveuniformity of etching across a surface of the wafer.

The pedestal 20 is supported by a support 104. A refrigerant passage 104a is formed inside the support 104. A refrigerant inlet pipe 104 b and arefrigerant outlet pipe 104 c are connected to the refrigerant passage104. A cooling medium output from a chiller 107 such as cooling waterand brine circulates through the refrigerant inlet pipe 104 b, therefrigerant passage 104 a and the refrigerant outlet pipe 104 c. Therefrigerant serves to draw the heat away from the pedestal 20 and theelectrostatic chuck 106 and to cool the pedestal 20 and theelectrostatic chuck 106.

A heat transfer gas supply source 85 supplies a heat transfer gas suchas helium gas (He) or argon gas (Ar) to a back surface of the wafer W onthe electrostatic chuck 106 through a gas supply line 130. Such aconfiguration allows a temperature of the electrostatic chuck 106 to becontrolled by the refrigerant flowing through the refrigerant passage104 a and the heat transfer gas supplied to the back surface of thewafer W. As a result, the temperature of wafer W can be controlled so asto have a predetermined temperature. The heat transfer gas supply source85 and the gas supply line 130 are an example of a heat transfer gassupply mechanism to supply the heat transfer gas to the back surface ofthe wafer W.

A power supply device 30 for supplying superimposed power of twofrequencies is connected to the pedestal 20. The power supply device 30includes a first radio frequency power source 32 that supplies firstradio frequency power (radio frequency power for generating plasma) of afirst frequency and a second radio frequency power source 34 forsupplying second radio frequency power (radio frequency power forgenerating a bias voltage) of a second frequency that is lower than thefirst frequency. The first radio frequency power source 32 iselectrically connected to the pedestal 20 through a first matching box33. The second radio frequency power source 34 is electrically connectedto the lower electrode 20 through a second matching box 35. For example,the first radio frequency power source 32 supplies the first radiofrequency power of 60 MHz to the pedestal 20. For example, the secondradio frequency power source 34 supplies the second radio frequencypower of 13.56 MHz to the pedestal 20. Here, although the first radiofrequency power is supplied to the pedestal 20 in the embodiment, thefirst radio frequency power may be supplied to the gas shower head 25.

The first matching box 33 causes load impedance of the first radiofrequency power source 32 to match internal (or output) impedancethereof. The second matching box 35 causes load impedance of the secondradio frequency power source 34 to match internal (or output) impedancethereof. The first matching box 33 serves to cause the load impedance ofthe first radio frequency power source 32 to appear the same as theinternal impedance thereof when plasma is generated in the chamber 10.The second matching box 35 serves to cause the load impedance of thesecond radio frequency power source 34 to appear the same as theinternal impedance thereof when plasma is generated in the chamber 10.

The gas shower head 25 is attached to the chamber 10 through a shieldring 40 covering a peripheral side wall thereof so as to close anopening of a ceiling part of the chamber 10. The gas shower head 25 maybe electrically grounded as illustrated in FIG. 1. Moreover, byconnecting a variable direct current power source to the shower head 25,a predetermined direct current (DC) voltage may be applied to the showerhead 25.

A gas introduction port 45 for introducing a gas is formed in the gasshower head 25. The gas shower head 25 includes a diffusion chamber 50 aprovided on a central side and a diffusion chamber 50 b provided on anedge side therein, which are diverged from the gas introduction port 45.The gas supplied from a gas supply source 15 is supplied to thediffusion chambers 50 a and 50 b through the gas introduction port 45,and diffuses across each of the diffusion chambers 50 a and 50 b. Then,the gas is introduced toward the pedestal 20 from many gas supply holes55.

An exhaust port 60 is formed in a bottom surface of the chamber 10, andthe chamber 10 is evacuated by an exhaust device 65 connected to theexhaust port 60. Thus, the inside of the chamber 10 can be maintained ata predetermined degree of vacuum. A gate valve G is provided at a sidewall of the chamber 10. The gate valve G opens and closes a carry-in/outopening when carrying the wafer in/out of the chamber 10.

The etching apparatus 1 includes a control unit 100 configured tocontrol the operation of the entire apparatus. The control unit 100includes a CPU (Central Processing Unit) 105, a ROM (Read Only Memory)110 and a RAM (Random Access Memory) 115. The CPU 105 performs a desiredprocess such as the etching process described later in accordance with arecipe stored in these memory areas. The recipe specifies controlinformation of the apparatus corresponding to process conditions such asprocess time, a pressure (evacuation of the gas), radio frequency powerand voltage, various gas flow rates, temperatures inside the chamber 10(an upper electrode temperature, a side wall temperature of the chamber10, a temperature of the wafer W (a temperature of the electrostaticchuck 106) and the like), and a temperature of the refrigerant outputfrom the chiller 107. Here, the recipe specifying programs and processconditions thereof may be stored in a hard disk or a semiconductormemory. Furthermore, the recipe may be set in a predetermined positionof the memory area in a state of being stored in a portable computerreadable storage medium such as a CD-ROM, a DVD and the like.

When performing an etching process, open and close of the gate valve Gis controlled, and a wafer W is carried into the chamber 10 and placedon the pedestal 20. The direct current voltage source 12 applies adirect current voltage HV to the chuck electrode 106 a, therebyattracting and holding the wafer W on the electrostatic chuck 106 byCoulomb's force.

Next, a gas for etching and radio frequency power are supplied to thechamber 10, thereby generating plasma. A plasma etching process isperformed on the wafer by the generated plasma. After the etchingprocess, the direct current voltage source 112 applies a DC voltage HVhaving an opposite sign to the DC voltage applied to the chuck electrode106 a while attracting the wafer W to the chuck electrode 106 a in orderto eliminate the charge of the wafer W, thereby removing the wafer Wfrom the electrostatic chuck 106. The open and close of the gate valve Gis controlled, and the wafer W is carried out of the chamber 10.

[Etching Process]

Next, an etching process according to an embodiment, which is performedon a silicon oxide film (SiO₂) by using the etching apparatus 1 havingthe configuration described above, is described below. As shown in FIG.2A, a silicon oxide film 6, which is an example of a film to be etched,is formed on a wafer W, and a mask film 5 is provided on the siliconoxide film 6. A polysilicon film, an organic film, an amorphous carbonfilm, a titanium nitride (TiN) film or the like can be used as the maskfilm 5.

In the etching method according to the embodiment, the etching isperformed under an extremely low temperature environment in which thesurface temperature of the wafer W is lower than −35 degrees C. Thisallows the etching process to be performed at an etching rate higherthan the etching rate achieved in the etching process performed whilekeeping the surface temperature of the wafer W at room temperature(e.g., about 25 degrees C. or higher). However, in the plasma etchingunder the extremely low temperature, the etching rate rapidly decreaseswhen the surface temperature of the wafer W rises. Hence, temperaturecontrol of the surface of the wafer W is very important.

FIG. 2A shows a result of examples of having performed etching processesunder the following process conditions in an extremely low temperatureenvironment.

Process Conditions:

-   Temperature (setting temperature of the chiller 107) : −60 degrees    C.-   Pressure: 60 mT (8.00 Pa)-   First Radio Frequency Power HF: 2500 W-   Second Radio Frequency Power LF: Shown in FIG. 2B (continuous wave,    pulse wave)-   Gas Types: Hydrogen (H₂)/Carbon Tetrafluoride (CF₄).

In the above process conditions, the surface temperature of the wafer Wduring the process was monitored. The leftmost column of “LF PULSE WAVE”in FIG. 2A shows an etching result of an example of having supplied thesecond radio frequency power LF having pulse waves of 4000 W, 0.3 kHz,and a duty cycle of 50 %. In this case, the surface temperature of thewafer W during the etching was set at −47 degrees C., and the etchingrate (ER) was 1259 nm/min. The effective value of the second radiofrequency power LF at this time was 2000 W.

The column of “LF CONTINUOUS WAVE” in FIG. 2A shows results of examplesof having supplied the second radio frequency power LF having continuouswaves of 4000 W, 2000 W and 1000 W under the above conditions. In thesecond radio frequency power LF having the continuous waves of 2000 W,the surface temperature of the wafer W during the etching was −43degrees C., and the etching rate was 865 nm/min. According to theresult, when the effective value was set at the same 2000 W as the aboveexample, by changing the second radio frequency power from thecontinuous waves to the pulse waves, the etching rate in the pulse waveswas about one-and-a-half times as high as that in the continuous waves(=1259/865).

However, in the second radio frequency power LF having the continuouswaves of 4000 W, the surface temperature of the wafer W during theetching (at center) was −35 degrees C., and the etching rate was 310nm/min, in which a phenomenon of an sluggish etching (which is alsohereafter referred to as an “etch stop”) occurred. In other words, theresult indicates that in the plasma etching under the extremely lowtemperature etching, there is an area where the surface temperature ofthe wafer W rapidly rises due to heat input and the etch stop occurswithout progress of etching.

In the second radio frequency power LF having the continuous waves of1000 W, the surface temperature of the wafer W during the etching was−49 degrees C., and the etching rate (ER) was 1256 nm/min. Thus, bykeeping the process temperature at the extremely low temperature lowerthan −35 degrees C., the etch stop can be prevented. Moreover, in theextremely low temperature area, the heat input decreases and the etchingrate increases as the second radio frequency power LF is decreased.

Thus, in the extremely low temperature process according to theembodiment, the higher the second radio frequency power LF becomes, thelower the etching rate becomes due to the increase in heat input, andthe etch stop occurs when the second radio frequency power LF becomes4000 W. The result indicates that the etching result completely differsfrom the result of the room temperature process in which the etchingrate increases as the second radio frequency power LF increases.

In the result of FIG. 2A, the second radio frequency power LF having thepulse waves of 4000 W, 0.3 kHz, and a duty cycle of 50% showed almostthe same surface temperature of the wafer W and etching rate as those ofthe second ratio frequency LF having the continuous waves of 1000 W. Inother words, as shown in FIG. 2B, when the second radio frequency powerLF having the pulse waves was supplied, the surface temperature of thewafer W could be made lower than when the second radio frequency powerLF having the continuous waves of the same second radio frequency power(effective value) was supplied. Thus, it is noted that when the secondradio frequency power LF has the pulse waves, the etching can beperformed at a higher etching rate than when the second radio frequencypower LF has the continuous waves because the surface temperature of thewafer W can be controlled to become lower against the heat input fromthe plasma.

FIGS. 3A and 3B show the relationship among the second high frequencypower LF, the pressure of the back surface of the wafer W and thesurface temperature of the wafer W by control of a flow rate of a heattransfer gas (He gas). A graph in FIG. 3A shows temperature changes ofthe surface of the wafer W with respect to the second radio frequencypower LF when the pressure of the back surface of the wafer W is changedinto 5 Torr (666.6 Pa), 15 Torr (2000 Pa), 25 Torr (3333 Pa), and 40Torr (5333 Pa). A graph shown in FIG. 3B shows temperature changes ofthe surface of the wafer W with respect to the pressure of the backsurface of the wafer W when the second radio frequency power LF ischanged into 0 W, 1000 W, 2000 W, and 4000 W. The result has indicatedthat it is difficult to effectively prevent the increase in surfacetemperature of the wafer W only by the pressure control of the backsurface of the wafer W.

From the above discussion, the embodiment proposes an etching method ofperforming an etching process intermittently by providing a period whenpulse waves of the second radio frequency power LF is not supplied inetching the silicon oxide film 6 while the surface temperature of thewafer W is controlled to have an extremely low temperature. This canprevent the etch stop and facilitate the etching by preventing the rapidincrease in surface temperature of the wafer and by improving an etchingrate.

FIG. 4 illustrates an example of the etching method according to anembodiment. First, a temperature of a wafer surface is controlled tohave an extremely low temperature lower than −35 degrees C. (step S10).Next, a hydrogen-containing gas and a fluorine-containing gas aresupplied into the chamber 10 (step S12). For example, hydrogen gas (H₂)and carbon tetrafluoride are supplied into the chamber 10.

Next, the first radio frequency power source 32 is turned on and outputsfirst radio frequency power HF, and the radio frequency power for plasmaexcitation is supplied to the pedestal 20 (which may be referred to asan “on” state). Also, the second radio frequency power source 31 isturned on and outputs second radio frequency power LF, and the radiofrequency power for bias is supplied to the pedestal 20. Thus, thesilicon oxide film 6 is etched (step S14: first process). At this time,although the first radio frequency power HF may have any of continuouswaves and pulse waves, the second radio frequency power LF has the pulsewaves. Execution time for the first process (predetermined time) ispreferably 30 seconds or shorter.

Subsequently, after the elapse of the predetermined time, the siliconoxide film 6 is etched while the supply of the second radio frequencypower is stopped (off) (step S16: second process). The execution timefor the second process is preferably 5 seconds or longer as describedlater. The pressure inside the chamber 10 when performing the secondprocess may be in a low pressure state of 10 mT or lower.

As illustrated in FIG. 4, in the etching method according to theembodiment, the second radio frequency power is intermittently suppliedto the pedestal 20 by repeating an on-off state of the second radiofrequency power LF. At this time, a period of time when the second radiofrequency LF is supplied (on time) is referred to as “Ton”, and a periodof time when the second radio frequency LF is not supplied (off time),is referred to as “Toff.” In this case, the second radio frequency powerhaving pulse waves of a frequency of 1/(Ton+Toff) is supplied to thepedestal 20. Furthermore, the duty cycle is expressed by a ratio of theon time Ton relative to the total period of time of the on time Ton andthe off time Toff, which is Ton/(Ton +Toff).

Next, it is determined whether a number of repetitions of the on-offstate of the second radio frequency power LF exceeds a predeterminednumber (step S18). The predetermined number is a preliminarilydetermined number more than one. When the number of repetitions of theon-off supply of second radio frequency power LF is determined not to beover the predetermined number, the second radio frequency power LFhaving the pulse waves is supplied again, and the silicon oxide film 6is etched (step S20: first process). A series of processes of steps S16through S20 is repeated until the number of repetitions exceeds thepredetermined number, and the present process flow ends when the numberof repetitions of the second radio frequency power LF is determined tobe over the predetermined number.

FIG. 5 shows a result of an etching process of working examples of theetching method according to the embodiment. The leftmost column shows anetching result of a comparative example, and three columns on its rightside show three etching results of the working examples.

Process conditions of the etching of the comparative example and theetching of the working examples according to the embodiment are in thefollowing.

Process Conditions COMPARATIVE EXAMPLES

-   Temperature (setting temperature of the chiller 107) : −60 degrees    C.-   Pressure: 60 mT (8.00 Pa)-   First Radio Frequency Power: 2500 W-   Second Radio Frequency Power: 4000 W, 0.3 kHz, Duty Cycle 50%-   Gas Types: Hydrogen (H₂)/Carbon Tetrafluoride (CF₄)-   On Time: 60 seconds-   Off Time: Absent.

Process Conditions WORKING EXAMPLES

-   Temperature (setting temperature of the chiller 107) : −60 degrees    C.-   Pressure: 60 mT (8.00 Pa)-   First Radio Frequency Power: 2500 W-   Second Radio Frequency Power: 4000 W, 0.3 kHz, Duty Cycle 50%-   Gas Types: Hydrogen (H₂)/Carbon Tetrafluoride (CF₄)-   On Time: 15 seconds (×4) (repeated four times)-   Off Time: Present (60 seconds, 30 seconds, 15 seconds).

As a result, in the etching method according to the embodiment, theetching rate was about one-and-a-half times as high as the etching ratein the etching of the comparative example, and selectivity improved upto a value close to one-and-a-half as high as the selectivity of thecomparative example. This is because the input heat from plasmadecreased during the off time Toff and the increase in surfacetemperature of the wafer W during the on time can be reduced byregularly providing the off time of the second radio frequency power LFduring the etching process according to the etching method of theembodiment. As a result, the surface temperature of the wafer was keptin the extremely low temperature state of a temperature lower than −35degrees C.

FIG. 6 shows an etching result of a working example of having set theoff time Toff at 5 seconds of the process conditions of theabove-mentioned working examples. The process conditions other than theoff time were the same. As a result, when the off time was set at 5seconds, in the etching method of the working example, the etching rateand the selectivity further improved, and both of the etching rate andthe selectivity were approximately one-and-a-half times as high as thoseof the comparative example.

FIG. 7 shows a surface temperature of a wafer W after the wafer W wascarried into the etching apparatus 1 and then etched by the etchingmethod of the working example and until the wafer W was carried out ofthe etching apparatus 1. When the first and second radio frequency powerwas supplied to the pedestal 20 while the wafer W was held on theelectrostatic chuck 106, plasma was generated and an etching processstarted. When the plasma was generated by supplying the first frequencypower and the second radio frequency power to the pedestal 20, thesurface temperature of the wafer W sharply increased in 5 seconds due tothe heat input from the plasma (plasma on), and then gently increased.

When the supply of the second radio frequency power was stopped duringthe etching, the surface temperature of the wafer W sharply decreased in5 seconds. This is because an amount of the input heat from the plasmadecreases. From the result, a period when the second radio frequencypower LF is not supplied just has to be 5 seconds or more.

Based on the etching result shown in FIGS. 2A and 2B, the off time Toffof the second radio frequency power LF may be in a range from 5 to 60seconds. However, considering throughput, the off time Toff of thesecond radio frequency power LF is preferably set at a short time.Hence, the off time Toff of the second radio frequency power ispreferably set in a range of 5 to 30 seconds, and more preferably set ina range of 5 to 10 seconds.

In the temperature transition shown in FIG. 7, the supply of the secondradio frequency power LF was stopped, the wafer W was carried out.Because of this, the surface temperature of the wafer W increased afterthe supply of the second radio frequency LF was stopped by turning offthe second radio frequency power source 34. However, in the etchingmethod according to the embodiment, an on-off of the second radiofrequency power LF is repeated a plurality of times. Moreover, theon-off of the second radio frequency power LF is repeated the pluralityof times (i.e., during the etching), and the supply of the refrigerantfrom the chiller 107 is not stopped. By doing this, the surfacetemperature of the wafer W can be maintained at the extremely lowtemperature lower than −35 degrees C. This causes the etching rate to beincreased, and for example, the etching method according to theembodiment is preferable for a process of forming a narrow hole havingan aspect ratio of 20 or higher by etching.

In the embodiment, the period of time for stopping the supply of thesecond radio frequency power LF having the pulse waves is provided instep S16 of FIG. 4. Instead of this, a period of time for stopping thesupply of the first radio frequency power HF and the supply of thesecond radio frequency power LF together may be provided. By doing this,during the off time of the first radio frequency power HF and the secondradio frequency power LF, the surface temperature of the wafer W can bemaintained at an extremely low temperature by decreasing the heat inputfrom the plasma, thereby increasing the etching rate and facilitatingthe etching.

FIG. 8 shows etching results of working examples according to theetching methods of the embodiment when changing a single on time Ton inthe process conditions, with an etching result of a comparative exampleperformed under process conditions of the comparative example (i.e.,without the off time Toff). In the etching of the working examples, theoff time Toff was set at 60 seconds, and the on time Ton was set at 30seconds (×2), 15 seconds (×4), and 5 seconds (×12). The etching resultsthereof are shown in FIG. 8. From the results, it is noted that theetching rate and the selectivity of any of the working examples werebetter than the etching result of the comparative example, and inparticular, that the etching was facilitated with increasing number ofon-off repetitions.

FIG. 9 shows etching results of working examples according to theetching method of the embodiment when changing an effective value of thesecond radio frequency power LF during the on time Ton among the processconditions, with an etching result of a comparative example performedunder process conditions of the comparative example (i.e., without theoff time Toff). In the working examples, the off time Toff was set at 30seconds; the on time Ton was set at 15 seconds (×4); and the secondradio frequency power LF was set at 2000 W (0.3 kHz, duty cycle 50%),4000 W (0.3 kHz, duty cycle 50%), and 6000 W (0.3 kHz, duty cycle 50%).The results indicate that the etching rate and the selectivity of any ofthe working examples according to the etching method of the embodimentwere better than those of the comparative example without generating theetch stop. From the results, because an effective value of the secondradio frequency power LF of 2000 W (0.3 kHz, duty cycle of 50%) is 1000W, the effective value of the second radio frequency power LF ispreferably higher than or equal to 1000 W (higher than or equal to 1.4W/cm² per unit area).

As discussed above, in the etching method according to the embodiment,by intermittently providing a period of time for stopping the supply ofthe second radio frequency power LF at each predetermined time intervalduring the etching, the surface temperature of the wafer W can bereduced and kept at an extremely low temperature. Thus, the etching rateand the selectivity can be improved. Moreover, even in an area of thesecond radio frequency power LF where the etch stop occurs during theetching when the off time of the second radio frequency power LF is notprovided, the etching can be facilitated in the extremely lowtemperature by intermittently providing the off time of the second radiofrequency power LF.

(Amount of Drawn Heat Caused by Cooling)

The chiller 107 circulates the refrigerant that is constantly controlledto have an extremely low temperature through the pedestal 20 during theetching. Accordingly, the heat is constantly drawn away from the surfaceof the wafer W during the etching. At this time, a total of an amount ofthe drawn heat (total amount of drawn heat) is calculated by multiplyingan amount of drawn heat per unit area by a period of time.

In the etching method according to the embodiment, when the total amountof drawn heat while stopping the output of the second radio frequencypower LF, is greater than or equal to 71.7 kW/m² ×5 seconds, the totalamount of drawn heat is sufficient. In the calculation of the amount ofdrawn heat, drawn heat performance of the chiller 107 is 5000 Ws, and adiameter of the pedestal 20 is 298 mm. In other words, the amount ofdrawn heat per unit area while stopping the output of the second radiofrequency power LF, just has to be less than or equal to 71.7 kw/m²(7.17 W/cm²). Here, when the outputs from the first radio frequencypower source 32 and the second radio frequency power source 34 areintermittently stopped, the amount of drawn heat per unit area whilestopping the outputs from the first radio frequency power source 32 andthe second radio frequency power source 34 just has to be 71.7 kW/m²(7.17 W/cm²) or lower per second.

As described above, according to the etching method of the embodiment,the etching rate can be enhanced, and the etching can be facilitated bysetting the surface temperature of the wafer W at a temperature lowerthan or equal to −35 degrees C., by intermittently supplying the radiofrequency power during the etching under the extremely low temperatureenvironment. Furthermore, according to the etching method of theembodiment, by intermittently supplying the radio frequency power to thepedestal 20 during the etching under the extremely low temperatureenvironment, the etching under the extremely low temperature can beperformed without causing the etch stop, and a process window can bebroadened. Thus, the etching method according to the embodiment ispreferably applied to the case where a hole having an aspect ratiohigher than or equal to 20 is intended to be etched more deeply, thecase where a narrower hole is intended be etched and the like.

[Temperature Control]

In the above-described etching method according to the embodiment, avery high etching rate ER can be achieved under the extremely lowtemperature environment in which the surface temperature of the wafer Wis lower than −35 degrees C. In other words, the temperature control ofthe surface of the wafer W is very important. For example, FIG. 10 showsa relationship between a temperature of the chamber 10 and an etchingrate ER of a silicon oxide film of working examples according to theextremely low temperature etching method. Etching results shown in FIG.10 are results of the etching of a silicon-containing antireflectionfilm under the following process conditions. The horizontal axis of FIG.10 shows process conditions of the wafer W (cases 1 through 4), and thevertical axis shows an etching rate (ER) at a central portion of thewafer W with a diameter of 300 mm.

Process Conditions:

-   Temperature (setting temperature of the chiller 107) : −60 degrees    C.-   Pressure: 60 mT (8.00 Pa)-   First Radio Frequency Power HF: 2500 W-   Second Radio Frequency Power LF: 4000 W, pulse wave of duty cycle    50% (effective value 2000 W)-   Gas Types: Hydrogen (H₂)/Tetrafluoride (CF₄).

In the above process conditions, Case 1 and Case 2 in FIG. 10 were caseswhere He gas (heat transfer gas) supplied to the back surface of thewafer W was controlled to have a pressure of 50 T (6666 Pa), and Case 3and Case 4 in FIG. 10 were cases where the pressure of He gas wascontrolled to have a pressure of 80 T (10666 Pa). Furthermore, in Case 1and Case 3 of FIG. 10, a temperature of a ceiling plate constituting thegas shower head 25 was set at 30 degrees C., and a side wall of thechamber 10 was set at 40 degrees C. In this case, when the pressure ofHe gas was set at 80 T, a cooling effect of the back surface of thewafer W by He gas was more increased than when the pressure of He gaswas set at 50 T, and the temperature of the wafer W could be maintainedat an extremely low temperature, thereby increasing the etching rate.

In Case 2 and Case 4 of FIG. 10, the temperature of the ceiling plateconstituting the gas shower head 25 was set at 150 degrees C., and thetemperature of the side wall of the chamber 10 was set at 150 degrees C.Even in this case, similarly to Case 1 and Case 3, when the pressure ofHe gas was set at 80 T, the cooling effect of the back surface of thewafer W by He gas was more increased than when the pressure of He gaswas set at 50 T, and the temperature of the wafer W could be maintainedat an extremely low temperature, thereby increasing the etching rate.

In other words, the temperature control of the surface of the wafer W isvery important under the extremely low temperature environment, and itis noted that controlling the surface temperature of the wafer W to havea temperature lower than −35 degrees C. has a great impact on theetching rate compared to the etching under the room temperatureenvironment.

Moreover, in addition to the cooling effect by the heat transfer gassuch as He gas, the heat input to the wafer W from the plasma can becontrolled by changing a parameter on the heat input side. This alsomakes it possible to set the surface temperature of the wafer W at anextremely low temperature and to increase the etching rate.

For example, FIG. 11 shows a relationship between control of the secondradio frequency power LF and the etching rate ER of a working example inthe etching method according to the embodiment. The etching resultsshown in FIG. 11 were result of the etching of the silicon-containingantireflection film under the following process conditions. Thehorizontal axis in FIG>11 shows process conditions of the wafer W, andthe vertical axis shows an etching rate (ER) at a central portion of thewafer W of a diameter of 300 mm.

Process Conditions:

-   Temperature (setting temperature of chiller 107): −70 degrees C.-   Pressure: 60 mT (8.00 Pa)-   First Radio Frequency Power HF: 2500 W-   Second Radio Frequency Power LF: as shown in FIGS. 2A and 2B (pulse    wave, continuous wave)-   Gas Types: Hydrogen (H₂)/Tetrafluoride (CF₄).

On the left side of FIG. 11, the second radio frequency power LF hadpulse waves of 4000 W and a duty cycle thereof was controlled to become50%. Hence, the effective value of the second radio frequency power LFon the left side of FIG. 11 was 2000 W. On the right side of FIG. 11,the second radio frequency power LF had continuous waves of 4000 W.Accordingly, the effective value of the second radio frequency power LFon the right side was 4000 W.

With reference to each of the plotted points, the etching rate on theleft side obtained by intermittently supplying the second radiofrequency power LF and by decreasing the surface temperature of thewafer W by limiting the heat input from the plasma while stopping thesupply of the second radio frequency power LF, was greatly higher thanthe etching rate on the right side.

As discussed above, the cooling effect of the back surface of the waferW can be increased by controlling the pressure of He gas, and bycontrolling the on-off state of the second radio frequency power source34. This allows the surface temperature of the wafer W to be maintainedat a temperature lower than −35 degrees C., thereby increasing theetching rate and the productivity.

[Temperature Control Unit]

As illustrated in FIG. 12, a temperature measurement unit 200 in anembodiment includes a control PC 201 configured to measure a temperatureof the focus ring 108 of the etching apparatus 1, and to control asurface temperature of a wafer W in real time based on the temperaturemeasurement result. The control PC 201 is an example of a monitormechanism to monitor the surface temperature of the wafer W in realtime. At this time, the control PC 201 controls the surface temperatureof the wafer W based on the result of the temperature measurement of thefocus ring 108.

Moreover, the temperature measurement unit 200 includes a temperaturemeasurement mechanism 205. The temperature measurement mechanism 205measures the temperature of the focus ring 108. By citing aninterferometer type thermometer illustrated in FIG. 13 as an example ofthe temperature measurement mechanism 205, a temperature measurementmethod of the focus ring 108 is described below. However, as long as thetemperature measurement mechanism 205 can measure the temperature of thefocus ring 108, instead of the interferometer type thermometer, anyknown temperature can be used as the temperature measurement mechanism205.

The temperature measurement mechanism 205 includes a spectroscope 202, alight source 203, a circulator 204, and a collimator 207. As illustratedin FIG. 12, a tip of an optical fiber 206 is provided under the focusring 108 of the etching apparatus 1 so as to be in close contact withthe focus ring 108 by being buried in the pedestal 20. The optical fiber206 is directly connected to the temperature measurement mechanism 205through the collimator 207.

As illustrated in FIG. 13, the temperature measurement mechanism 205measures the temperature of the focus ring 108 made of silicon (Si) withrefractive index of n. The focus ring 108 of a measurement object has afirst principal surface corresponding to the back surface of the focusring 108 and a second principal surface corresponding to the top surfaceof the focus ring 108.

First, the light source 203 emits spectral light with a wavelength of1560 nm. The light source 203 is a light source of measurement lightthat penetrates through the focus ring 108. The measurement light of1560 nm emitted from the light source 203 is input to the collimator 207through the circulator 204, converged and emitted from an output end ofthe optical fiber 206 toward the focus ring 108. First reflected light Aof the measurement light reflected from the first principal surface andsecond reflected light B of the measurement light reflected from thesecond principal surface after passing through the focus ring 108 enterthe collimator 207. The first reflected light A and the second reflectedlight B having entered the collimator 207 is transmitted to thespectroscope 202 by way of the circulator 204. Returning to FIG. 12, thecontrol PC 201 is connected to the spectroscope 202. The control PC 201measures the temperature of the focus ring 108 based on a waveformobtained by Fourier transform of interference intensity distributionbetween the first reflected light A and the second reflected light Btransferred from the spectroscope 202.

In this manner, in the embodiment, the temperature of the focus ring 108is measured by using the temperature measurement mechanism 205, and atemperature of the pedestal 20 holding the wafer W thereon is notdirectly measured. This is because when a temperature of the backsurface of the pedestal 20 is directly measured, the measurement valueof the back surface of the pedestal 20 does not indicate an actualsurface temperature of the wafer W and accurate temperature control ofthe wafer W becomes difficult due to a predetermined distance providedbetween the pedestal 20 and the wafer W. Moreover, when the temperaturemeasurement is performed at the back surface of the pedestal 20, thetemperature measurement is likely to be influenced by the heat inputfrom the plasma generated above the wafer W and by an electrical impactfrom the electrostatic chuck 106, which is likely to prevent theaccurate measurement of the surface temperature of the wafer W. Fromthese reasons, the temperature measurement unit 200 measures thetemperature of the focus ring 108, thereby estimating the surfacetemperature of the wafer W based on the measurement result.

On this occasion, the etching apparatus 1 includes a cooling mechanismthat cools the focus ring 108 and an attraction mechanism that attractsthe focus ring 108 on the electrostatic chuck 106 to be able toaccurately estimate the surface temperature of the wafer W from themeasurement temperature of the focus ring 108. These functions arespecifically described below with reference to FIGS. 14A and 14B.

FIG. 14A illustrates an example of a conventional electrostatic chuck106, a focus ring 108, and a neighboring portion thereof. In the exampleof FIG. 14A, an intermediary body 310 to be in close contact with theelectrostatic chuck 106 and the focus ring 108 through heat transmissionsheets 300 is provided between the electrostatic chuck 106 and the focusring 108. This causes the electrostatic chuck 106 to be thermallyseparated from the focus ring 108. As a result, in a configurationexample as illustrated in FIG. 14A, it is difficult to accuratelyestimate the surface temperature of the wafer W from the measuredtemperature of the focus ring 108.

In contrast, FIG. 14B illustrates the electrostatic chuck 106, the focusring 108 and a neighboring portion thereof of the etching apparatus 1according to the embodiment. In the etching apparatus 1 according to theembodiment, the intermediary body 310 and the heat transmission sheets310 are not provided between the focus ring 108 and the electrostaticchuck 106, and the focus ring 108 and the electrostatic chuck 106 aredirectly in contact with each other.

In addition, chuck electrodes 406 a and 406 b are provided inside theelectrostatic chuck 106 under the focus ring 108. A direct voltagesource 412 a is connected to the chuck electrode 406 a, and the directvoltage source 412 a applies a direct voltage HV-A to the chuckelectrode 406 a. Similarly, a direct voltage source 412 b is connectedto the chuck electrode 406 b, and the direct voltage source 412 bapplies a direct voltage HV-B to the chuck electrode 406 b. Thus, thefocus ring 108 is attracted on the electrostatic chuck 106 by Coulomb' sforce.

Furthermore, in the etching apparatus 1 according to the embodiment, agas supply line 430 is provided to supply a heat transfer gas such ashelium (He) gas or argon (Ar) gas to the back surface of the focus ring108. The heat transfer gas supply source 85 illustrated in FIG. 1 isconnected to the gas supply line 430. Thus, the back surface of thefocus ring 108 is cooled by the heat transfer gas similar to the backsurface of the wafer W. Also, the back surface of the focus ring 108 iscooled by a refrigerant flow passage 104 a similar to the back surfaceof the wafer W.

Because the etching apparatus 1 having such a configuration includes astructure for cooling the back surface of the focus ring 108 and theback surface of the wafer W under the same environment, the heat drawingperformance of the focus ring 108 and the pedestal 20 against the heatinput from the plasma during the etching can be made the same as eachother. Hence, by measuring the temperature of the focus ring 108, thesurface temperature of the wafer W can be accurately estimated based onconditions including a material and a structure of the pedestal 20, astructure of the refrigerant flow passage 104 a, and a temperature ofthe refrigerant. Thus, by measuring the temperature of the focus ring108 in real time, the surface temperature of the wafer W can bemonitored in real time.

Here, the mechanism of supplying the refrigerant to the refrigerant flowpassage 104 a from the chiller 107, and the mechanism of supplying theheat transfer gas from the heat transfer gas source 85 through the gassupply lines 130 and 430 to the back surface of the wafer W and thefocus ring 108 are an example of a temperature control mechanismprovided in the pedestal 20. The temperature measurement unit 200adjusts the surface temperature of the wafer W by using on-off controlof the temperature control mechanism and the radio frequency power RF.

More specifically, the control PC 201 in FIG. 12 acquires thetemperature of the focus ring 108 at each predetermined time interval inreal time. Then, the control PC 201 controls the on-off state of theradio frequency power RF from the acquired temperature information ofthe focus ring 108 in real time, based on a relational graph Gh1, whichis preliminarily stored in the memory unit such as the ROM 110, betweenthe output of the radio frequency power RF and the temperature of thewafer Was illustrated in FIG. 12. For example, when a temperatureindicated.by the acquired temperature information is higher than −35degrees C., the control PC 201 determines that the surface temperatureof the wafer W is not in the extremely low temperature state, andoutputs a signal to cause the control unit 100 to stop the supply of theradio frequency power RF in order to stop the supply of the radiofrequency power RF. The control unit 100 performs feedback control ofstopping the supply of the radio frequency power RF based on the signalsent from the control PC 201.

In addition, for example, when the temperature indicated by the acquiredtemperature information is lower than −35 degrees C., the control PC 201determines that the surface temperature of the wafer W is in theextremely low temperature state, and outputs a signal to cause thecontrol unit 100 to supply the radio frequency power RF in order tosupply the radio frequency power RF. The control unit 100 performsfeedback control of supplying the radio frequency power RF based on thesignal sent from the control PC 201. Thus, by supplying the radiofrequency power RF having pulse waves based on the measured temperatureof the focus ring 108 in real time, the surface temperature of the waferW can be maintained at an extremely low temperature that is lower than−35 degrees C.

The control PC 201 may control only the on-off state of the output ofthe second radio frequency power 34 as the radio frequency power RF, ormay control the on-off state of the output of the first radio frequencypower source 32 and the second radio frequency power source 34 insynchronization with each other.

As described above, the temperature measurement unit 200 performs thefeedback control to keep the surface temperature of the wafer W lessthan −35 degrees C. by stopping the output of the second radio frequencypower source 34 or the outputs of the first radio frequency power source32 and the second radio frequency power source 34 based on the measuredtemperature of the focus ring 108. The above-described feedback functionaccording to the embodiment allows the surface temperature of the waferW to be maintained at the extremely low temperature. In particular, theetching apparatus 1 according to the embodiment includes the temperaturecontrol mechanism (cooling mechanism and heat transfer mechanism) asillustrated in FIG. 14 under the focus ring 108 in order to control thetemperature of an edge portion of the wafer W. This enables the focusring 108 and the pedestal 20 to have the same heat drawing performance.Accordingly, by measuring the temperature of the focus ring 108, thesurface temperature of the wafer W can be precisely estimated. Thus, bymeasuring the temperature of the focus ring 108, the feedback controlcan be performed so that the surface temperature of the wafer W ismaintained at the extremely low temperature that is lower than −35degrees C.

Furthermore, in the embodiment, by measuring the temperature of thefocus ring 108, the feedback control of the pressure of the heattransfer gas can be performed so that the surface temperature of thewafer W is maintained at the extremely low temperature that is lowerthan −35 degrees C.

FIG. 15 shows a relationship between a heat transfer gas and atemperature of the focus ring 108 in an extremely low temperature of aworking example according to the embodiment. The horizontal axis in FIG.15 shows a pressure of He gas(FR He BP) when He gas is supplied to theback surface of the focus ring 108 as a heat transfer gas. The verticalaxis in FIG. 15 shows a temperature of the focus ring 108. According tothe result, it is noted that the pressure of He gas and the temperatureof the focus ring 108 have a relation of a graph shown in FIG. 15 in theextremely low temperature environment.

FIG. 16 shows a result of feedback control by the control PC 201 of aworking example. According to the result, by repeating the on-off stateof the radio frequency power RF, the surface temperature of the wafer Wincreasing while the radio frequency power RF is supplied is decreasedwhile the radio frequency power RF is not supplied. Thus, the surfacetemperature of the wafer W can be maintained at the extremely lowtemperature that is lower than −35 degrees C.

Because the on-off control of the radio frequency poser RF and thepressure control of the heat transfer gas are performed in real timedepending on the temperature measurement of the focus ring during theetching, temperature controllability is high. Hence, according to theetching apparatus 1 of the embodiments, by measuring the temperature ofthe focus ring 108, autonomous control of both of the on-off control ofthe radio frequency power RF and the pressure control of the heattransfer gas can be performed in real time. As a result, a high etchingrate can be achieved by maintaining the surface temperature of the waferW at the extremely low temperature that is lower than −35 degrees C.,thereby improving the productivity.

Here, the control PC 201 may control at least one of the pressurecontrol of He gas and the on-off control of the radio frequency powerRF. For example, the control PC 201 may control the stop of the outputof the first radio frequency power and the second radio frequency power,and the pressure control of the heat transfer gas may be performed bythe autonomous control.

Thus, according to the etching method and the plasma processingapparatus of the embodiments of the present invention, etching isfacilitated by temperature control in an extremely low temperature.

Hereinabove, although the etching method and the plasma processingapparatus have been described according to the embodiments, the etchingmethod and the plasma processing apparatus of the present invention isnot limited to the embodiments, and various modifications andimprovements can be made without departing from the scope of theinvention. Moreover, the embodiments and modifications can be combinedas long as they are not contradictory to each other.

For example, the above embodiments have been described by citinghydrogen gas as a hydrogen-containing gas and carbon tetrafluoride as afluorine-containing gas. However, the hydrogen-containing gas is notlimited to hydrogen gas (H₂), but the hydrogen-containing gas just hasto include at least one gas of methane (CH₄) gas, fluoromethane (CH₃F)gas, difluoromethane (CH₂F₂) gas, and trifluoromethane (CHF₃) gas. Also,the fluorine-containing gas is not limited to carbon tetrafluoride, butmay be C₄F₆ (hexafluoro-1,3-butadiene) gas, C₄F₈ (perfluorocyclobutane)gas, C₃F₈ (Octafluoropropane) gas, NF₃ (nitrogen trifluoride), and SF₈(sulfur hexafluoride).

Moreover, a process of removing a reaction product produced by anetching may be performed during the off time Toff of the second radiofrequency power, or during the off time of Toff of the first radiofrequency poser and the second radio frequency power. For example, bysupplying oxygen (O₂) gas during the off time Toff, O₂ plasma generatedfrom oxygen gas may serve to remove the reaction product attached to thetop opening of the hole. Otherwise, by supplying hydrogen (H₂) gas andcarbon fluoride (CF₄) gas, plasma generated from the mixed gas thereofmay facilitate the etching and remove the reaction product.

Furthermore, the plasma processing apparatus according to theembodiments of the present invention can be applied not only to acapacitively coupled plasma (CCP: Capacitively Coupled Plasma) apparatusbut also to other types of etching apparatuses. For example, the othertypes of plasma processing apparatus includes an inductively coupledplasma (ICP: Inductively Coupled Plasma) apparatus, a plasma processingapparatus using a radial line slot antenna, a helicon wave excitedplasma (HWP: Helicon Wave Plasma) apparatus, an electron cyclotronresonance plasma (ECR: Electron Cyclotron Resonance Plasma) apparatusand the like as examples.

In the present specification, a semiconductor wafer W has been describedas an etching object, but a variety of substrates used for a flat paneldisplay, a substrate for an EL (electroluminescence) device and thelike, a photomask, a CD substrate, and a printed substrate are availablefor the etching object.

What is claimed is:
 1. An etching method comprising steps of : etching asilicon oxide film by using plasma in a first condition in which asurface temperature of a substrate is controlled to have a temperaturelower than −35 degrees C., and the plasma is generated from ahydrogen-containing gas and a fluorine-containing gas by using firstradio frequency power output from a first radio frequency power sourceand second radio frequency power output from a second radio frequencypower source; and etching the silicon oxide film by using the plasma ina second condition in which the output of the second radio frequencypower from the second radio frequency power source is stopped, whereinthe steps of etching the silicon oxide film by using the plasma in thefirst condition and etching the silicon oxide film by using the plasmain the second condition are alternately repeated multiple times.
 2. Theetching method as claimed in claim 1, wherein the hydrogen-containinggas includes at least one of hydrogen gas, methaRe gas, fluoromethanegas, difluoromehtane gas, and trifluoromethane gas.
 3. The etchingmethod as claimed in claim 1, wherein the second radio frequency powerhas a value of 1.4 W/cm2 per unit area.
 4. A etching method comprisingsteps of: etching a silicon oxide film by using plasma in a firstcondition in which a surface temperature of a substrate is controlled tohave a temperature lower than −35 degrees C., and the plasma isgenerated from a hydrogen-containing gas and a fluorine-containing gasby using first radio frequency power output from a first radio frequencypower source and second radio frequency power output from a second radiofrequency power source; and etching the silicon oxide film by using theplasma in a second condition in which the output of the first radiofrequency power from the first radio frequency power source and theoutput of the second radio frequency power from the second radiofrequency power source are stopped, wherein steps of etching the siliconoxide film by using the plasma in the first condition and etching thesilicon oxide film by using the plasma in the second condition arealternately repeated multiple times.
 5. The etching method as claimed inclaim 4, wherein the hydrogen-containing gas includes at least one ofhydrogen gas, methane gas, fluoromethane gas, difluoromehtane gas, andtrifluoromethane gas.
 6. The etching method as claimed in claim 4,wherein the second radio frequency power has a value of 1.4 W/cm2 perunit area.
 7. A plasma processing apparatus, comprising: a pedestal toreceive a substrate thereon; a temperature control mechanism provided inthe pedestal; a heat transfer gas supply mechanism configured to supplya heat transfer gas to aback surface of the substrate; a first radiofrequency power source configured to output first high frequency powerhaving a first frequency; a second radio frequency power sourceconfigured to output second high frequency power having a secondfrequency that is lower than the first frequency; and a temperaturemeasurement unit configured to control a surface temperature of thesubstrate to have a temperature lower than −35 degrees C. by using thetemperature control mechanism provided in the pedestal and to performfeedback control of stopping the output of the second radio frequencypower from the second radio frequency power source.
 8. The plasmaprocessing apparatus as claimed in claim 7, wherein both of the firstradio frequency power and the second radio frequency power have pulsewaves or the second radio frequency power has pulse waves.
 9. The plasmaprocessing apparatus as claimed in claim 7, wherein the stop of theoutput of the second radio frequency power from the second radiofrequency power source, and pressure control of the heat transfer gas,are performed by autonomous control.
 10. The plasma processing apparatusas claimed in claim 7, further comprising: a monitor mechanismconfigured to monitor the surface temperature of the substrate in realtime.
 11. The plasma processing apparatus as claimed in claim 10,further comprising: a focus ring provided on a periphery of thepedestal, wherein the monitor mechanism is configured to monitor thesurface temperature of the substrate based on a result of temperaturemeasurement of the focus ring.
 12. The plasma processing apparatus asclaimed in claim 11, wherein the temperature measurement unit measuresthe surface temperature of the substrate by using an interferometer typethermometer.
 13. The plasma processing apparatus as claimed in claim 7,further comprising: a focus ring provided on a periphery of thepedestal, wherein the temperature measurement unit performs the feedbackcontrol so that the focus ring has a temperature lower than −35 degreesC. by stopping the output of the second radio frequency power from thesecond radio frequency power source.
 14. A plasma processing apparatus,comprising: a pedestal to receive a substrate thereon; a temperaturecontrol mechanism provided in the pedestal; a heat transfer gas supplymechanism configured to supply a heat transfer gas to a back surface ofthe substrate; a first radio frequency power source configured to outputfirst high frequency power having a first frequency; a second radiofrequency power source configured to output second high frequency powerhaving a second frequency that is lower than the first frequency; and atemperature measurement unit configured to control a surface temperatureof the substrate to have a temperature lower than −35 degrees C. byusing the temperature control mechanism provided in the pedestal and toperform feedback control of stopping the output of the first radiofrequency power from the first radio frequency power source and theoutput of the second radio frequency power from the second radiofrequency power source. 25
 15. The plasma processing apparatus asclaimed in claim 14, wherein both of the first radio frequency power andthe second radio frequency power have pulse waves or the second radiofrequency power has pulse waves.
 16. The plasma processing apparatus asclaimed in claim 14, wherein the stop of at least one of the output ofthe first radio frequency power from the first radio frequency powersource and the output of the second radio frequency power from thesecond radio frequency power source, and pressure control of the heattransfer gas, are performed by autonomous control.
 17. The plasmaprocessing apparatus as claimed in claim 14, further comprising: amonitor mechanism configured to monitor the surface temperature of thesubstrate in real time.
 18. The plasma processing apparatus as claimedin claim 17, further comprising: a focus ring provided on a periphery ofthe pedestal, wherein the monitor mechanism is configured to monitor thesurface temperature of the substrate based on a result of temperaturemeasurement of the focus ring.
 19. The plasma processing apparatus asclaimed in claim 18, wherein the temperature measurement unit measuresthe surface temperature of the substrate by using an interferometer typethermometer.
 20. The plasma processing apparatus as claimed in claim 7,further comprising: a focus ring provided on a periphery of thepedestal, wherein the temperature measurement unit performs the feedbackcontrol so that the focus ring has a temperature lower than −35 degreesC. by stopping the output of the first radio frequency power from thefirst radio frequency power source and the output of the second radiofrequency power from the second radio frequency power source.